Interpretive Summary: The impact of erosion on soil and carbon loss and redistribution within landscapes is an important component for developing estimates of carbon sequestration potential, management plans to maintain soil quality, and transport of sediment bound agrochemicals. Soils of the Southeastern U.S. Coastal Plain are typically low in carbon content and susceptible to erosive soil and carbon loss during periods of intensive convective storms following agricultural activities. We used a variable intensity rainfall simulation pattern to quantify the effects of tillage (conventional and strip) and soil water content on sediment-bound carbon and nitrogen loss from an Ultisol soil in Tifton, GA. Soil water content prior to the rainfall event did not affect sediment loss within either tillage treatment, but losses from conventionally tilled treatments were greater than from strip till. Sediment lost from all treatments was higher in carbon relative to the top 2 cm of soil, ranging from 0.9 - 7 times higher for conventional till and from 0.6 - 4 times higher for strip till. Because conventional till treatments lost much more sediment than strip till, 3 - 5 times more carbon was lost during the simulated rainfall events. Eroded nitrogen loss was proportional to carbon loss in both tillages, but organic matter lost from strip till treatments had a higher nitrogen content than conventional till. Results suggest that even though sediment eroded from strip till treatments has higher organic nitrogen concentrations, the decreased erosion from strip tillage serves to increase retention of nitrogen within the landscape as compared to conventional tillage.

Technical Abstract:
The impact of erosion on soil and carbon loss and redistribution within landscapes is an important component for developing estimates of carbon sequestration potential, management plans to maintain soil quality, and transport of sediment bound agrochemicals. Soils of the Southeastern U.S. Coastal Plain are typically low in carbon content and susceptible to erosive soil and carbon loss during periods of intensive convective storms following agricultural activities. Rainfall simulation experiments are frequently used to estimate erosion and carbon loss potentials, but methods used to quantify carbon and nitrogen pools during such experiments have not been consistent. We used a variable intensity rainfall simulation pattern to quantify the effects of tillage (conventional and strip) and antecedent soil water content on sediment-bound carbon and nitrogen loss from an Ultisol soil. Field plots (2 m x 3 m) were established on each treatment and received 60 mm of simulated rainfall over a 70 min period with peak rainfall rate at 160 mm h-1 for a duration of 20 min. Antecedent water treatment was ~12 mm of simulated rainfall added 24 h prior to each simulated event. We also quantified carbon and nitrogen loss via erosion of silt + clay sized versus sand sized sediment particles. Antecedent soil water content had no effect on sediment loss within either tillage treatment, but losses from conventionally tilled treatments were significantly greater than from strip till. Sediment lost as silt + clay ranged from 58 - 78% of total sediment loss under conventional tillage and from 30-39% under strip tillage. The fraction of sediment lost as silt + clay versus sand was greater under conventional tillage than under strip tillage. Sediment lost from all treatments was enriched in carbon relative to the top 2 cm of soil. Within-event carbon enrichment ranged from 0.9 - 7.2 for conventional till and from 0.6 - 3.7 for strip till. The silt + clay fraction of the strip till treatment had significantly higher carbon content than both the strip till sand fraction and the silt + clay fraction of the conventional till treatment. Carbon loss from all treatments was directly proportional to sediment loss. However, due to the higher proportion of sand sized particles and lower total sediment loss in the strip till treatments, conventional till treatments lost 4.6 - 6 times more carbon from the silt + clay sized fraction and 1.9 - 4.8 times more carbon from the sand sized fraction than did strip till treatments. Results suggest that the higher proportion of silt + clay fraction sediment loss from CT continually depletes nitrogen enriched organic matter, while the decreased erosion from ST serves to increase retention of organic nitrogen within the landscape. An approach that adjusts loss estimates of organic carbon and nitrogen by using wet-sieved sub-samples for analysis followed by standardization against total bulk sediment loss accounts for introduced errors from both sub-sampling efficiency and disturbance.